Data prefetching efficiently reduces the memory access latency in NUCA architectures as the Last Level Cache (LLC) is shared and distributed across multiple cores. But cache pollution generated by prefetcher reduces its efficiency by causing contention for shared resources such as LLC and the underlying network. The paper proposes Zero Pollution Prefetcher (ZPP) that eliminates cache pollution for NUCA architecture. For this purpose, ZPP uses L1 prefetcher and places the prefetched blocks in the data locations of LLC where modified blocks are stored. Since modified blocks in LLC are stale and request for such blocks are served from the exclusively owned private cache, their space unnecessary consumes power to maintain such stale data in the cache. The benefits of ZPP are (a) Eliminates cache pollution in L1 and LLC by storing prefetched blocks in LLC locations where stale blocks are stored. (b) Insufficient cache space is solved by placing prefetched blocks in LLC as LLCs are larger in size than L1 cache. This helps in prefetching more cache blocks, thereby increasing prefetch aggressiveness. (c) Increasing prefetch aggressiveness increases its coverage. (d) It also maintains an equivalent lookup latency to L1 cache for prefetched blocks. Experimentally it has been found that ZPP increases weighted speedup by 2.19x as compared to a system with no prefetching while prefetch coverage and prefetch accuracy increases by 50%, and 12%, respectively compared to the baseline. 1

Applications running on Network on Chip (NoC) based multicore systems demand increased on-chip network bandwidth that can cater to the need for intensive communication among the cores and caches. Due to strict area and power budget, the bandwidth offered by NoC is very limited. Data-intensive and communication-centric applications on encountering a cache miss lead to a considerable burden on the underlying network for transferring blocks from multiple cache hierarchies to the requesting core as packets. This increases the packet transmission latency, thereby slowing down the system performance. Also, NoC being the highest component of power consumption after the cores, an increase in packets increases the dynamic power consumption of NoC. The article proposes FlitZip that addresses the problem by reducing on-chip traffic through compressing network packets. Hence, the compressed packet requires less bandwidth during its transfer, reducing the network's power consumption. Experimental analysis shows that FlitZip achieves a better compression ratio of 52 percent, reduces packet latency and bandwidth utilization by 19.28 and 27 percent, respectively. It also reduces the area and power consumption of the de/compression units by 53.33 and 62.3 percent, respectively, compared to the state-of-the-art packet compression technique, NoΔ.

Prefetching helps in reducing the memory access latency in multi-banked NUCA architecture, where the Last Level Cache (LLC) is shared. In such systems, an application running on core generates significant traffic on the shared resources, the underlying network and LLC. While prefetching helps to increase application performance, but an inaccurate prefetcher can cause harm by generating unwanted traffic that additionally increases network and LLC contention. Increased network contention results in untimely prefetching of cache blocks, thereby reducing the effectiveness of a prefetcher. Prefetch accuracy is extensively used to reduce unwanted prefetches that can mitigate the prefetcher caused contention. However, the conventional prefetch accuracy parameter has major limitations in NUCA architectures. The article exposes that prefetch accuracy can create two major false-positive cases of prefetching, Under-estimation and Over-estimation problems, and false feedback loop that can mislead a prefetcher in generating more unwanted traffic. We propose a novel technique, Coordinated Prefetching for Efficient (COPE), which addresses these issues by redefining prefetch accuracy for such architectures and identifies additional parameters that can avoid generating unwanted prefetch requests. Experiment conducted using PARSEC benchmark on a 64-core system shows that COPE achieve 3% reduction in L1 cache miss rate, 12.64% improvement in IPC, 23.2% reduction in average packet latency and 18.56% reduction in dynamic power consumption of the underlying network.